US2372451A - Apparatus for measuring or indicating the roughnesses or undulations of surfaces - Google Patents

Description

Mmh 27, 1945. R. a REASON 2,372,451

- APPARATUS FQR MEASURING on INDIGATING THE ROUGHNESSES OR UNDULATI ONS 0F SURFACES Filed July 15. 1943 2 Sheets- Sheet 1" March 27, 1945. I REASON 2,372,451

, APPARATUS FOR MEASURING OR INDICATING THE ROUGHNESSES OR UNDULATIONS OF SURFACES Filed July 15, 1943 2 Sheets-Sheet 2 7 v J ,1 J L i f Inventor .ments normal or approximately normal Patented Mar. 27, 1945 A APPARATUS FOR MEASURING OR INDICAT- ING THE ROUGHNE TIONS OF SURFACES Richard Edmund Reason, Leicester, England, as-

signor to Taylor, Taylor & Hobson Limited, Leicester, England, a company of Great Britain Application July 15, 1943, Serial No. 494,873

In Great Britain May 18, 1942 Claims.

This invention relates to apparatus for measuring or indicating the roughnesses orundulations of a surface, of the kind in which a stylus is traversed over the surface and controls a measuring device in accordance with its moveto the surface during such traversing.

In the specifications of U. S. A. patent aplications Serial Nos. 381,920 (filed March 5, 1941) 378,836 (filed February 13, 1941), and 379,536 (filed February 18, 1941), apparatus of this kind is described wherein a pick-up unit incorporating the stylus is carried on an arm projecting from a casing which is adjustably mounted on a stand and contains mechanism for driving the arm (and thus traversing the stylus over the surface) at any one of a plurality of different speeds,

such unit being employed in conjunction with a. pen recorder for giving a trace of a section of the surface and with an integrating meter for giving a measure of the average roughness of a portion of the surface, a relatively slow speed of traverse being utilised for operating the pen recorder and a relatively fast speed for operating the average" meter.

The present invention has for its primary objeot to provide a simplified form of apparatus incorporating a portable pick-up unit which can be brought by hand into engagement withthe surface and is connected to the rest of the apparatus merely by a flexible electric lead, the

unit being more especially intended for use on cylindrical surfaces although also capable of use in other surfaces. For many purposes it will sufiice to provide an "avei'age measurement alone, the pen recorder being omitted or alternatively to employ only a pen-recorder without an average meter, and the invention readily lends itself to such simple cases as well as to more elaborate instances in which both kinds of measurement are required.

With such a simplified unit it is necessary to provide adequate protection from damage for the stylus and for the detector device which transforms the stylus movements into electricalenergy, and to prevent errors from arising as the result of irregular hand pressure on the unit. In particular, it is desirable to provide 'one or more skids'on the unit which can run over the surface or an auxiliary surface and afford a. datum or zero for the stylus movements perrnal to the surface. Ifsuch skids are located close to the stylus, serious errors in measurement can readily arise fromfailure to steer'the unit properly along the surface, whilst-on the SSE-S 0R UNDULA- other hand if such skids are relatively widely spaced to avoid risk of such errors, other errors may arise since without careful z't'justment the skids may not locate the stylus within its operative range of movement.

These difliculties are obviated in the 'construction of a pick-up unit according to the present invention, which comprises a pick-up head provided with a stylus for engaging the cylindrical or other test surface and with means affording a datum for the stylus movements, at light supporting framework therefore having relatively widely spaced supporting elements which are held in engagementwith the test surface, and means for adjusting the pick-up head relatively to the supporting elements of the framework in a direction approximately normal to the test surface, the supporting element being so arranged that, when the apparatus is applied to the investigation of a cylindrical surface, measuring movements of the stylus in all positions of adjustment of the ick-up head are constrained to take place along a 'line which intersects the axis of the cylindrical surface or passes close .thereto.

The datum for the stylus movement may be provided by means of one or more skids mounted on the pick-up headclose to the stylus and engagingwith the test surface. Alternatively the invention of the present applicants copending U. S. A. patent application Serial No. 458,560

' (filed September 16, 1942) may be incorporated into the unit. Thus the datum for the stylus movements may be provided by means of a. guiding device having two relatively movable elements, one of which is carried by the pick-up head whilst the other remains stationary during traversing of the stylus over the test surface, one of such elements being constituted by a reference surface set sothat a line on it is maintained substantially parallel to the testsurface in the direction of traversing, whilst the other is constituted by a skid cooperating with the reference surface along such line.

, The arrangement of the-supporting elements of the framework may vary to suit the type of test surface on which it is to rest. Thus for a. frame work suitable for use on either plane or cylindrical surfaces, the supporting elements may conveniently be so shaped as to engage with the test surface at points lying on 'two parallel lines. For example the supporting elements may consist of or constitute a v-groove or parts of 'a. discontinuousV-groove, for use with a convex cylindrical surface, or may consist of a pair of Parallel rails'orof'parts-of a pair of discon- When this arrangement is employed for obtaining an average measurement, the electrical circuit controlling the average meter includes limit contacts G in the casing E directly operated by the movement of the driving rod G, so that the average meter is energised for an accurately predetermined time. A very short traversing movement is amply suflicient to obtain the desired average measurement, and only quite small clearances are required for the pick-up head movement within the length of the framework A. The provision of a traversing drive within the casing makes it possible to obtain a satisfactory graph on a pen-recorder, provided that the casing is held stationary throughout the movement. 4

If desired, instead of providing skids on the lower side of the pick-up head to run on the test surface itself, the pick-up head may carry a skid running on an optically fiat reference surface carried by the stationary framework or otherwise held stationary in such a position as to lie accurately parallel to the test surface in the direction of traversing. Alternatively, such ref erence surface may be carried by the pick-up in the direction of their length, it is desirable to provide some free play between the nut B and the rod B, in conjunction with a spring B The casing E containing the mechanism for driving the pick-up head C, is attached to the crossbar B between the links J, and in the example shown a modified form of driving mechanism is illustrated. In this case, thedrive is obtained from a small electric motor within the casing E, this motor driving a heart-shaped cam K, withwhich a roller K carried by the pick-up head engages, the ligament springs J 1 serving to hold the roller K in engagement with the cam head for engagement by a stationary skid. Other modifications analogous to those described in the specification of copending application Serial No. 458,560 above mentioned can alternatively be employed.

The shape of the framework A may be modified in a variety of ways. Thus instead of having a pair of V-grooves in its end walls, the framework may reston a continuous V-groove extending throughout its length as shown at A in Figures 4 and 5 with a slit A along the ridge of the V, through which the stylus D can project.- Again instead of or in addition to using a continuous or discontinuous V-groove, a pair of parallel rails A as shown in Figures 7 and 8 (either continu- 0115 or discontinuous) may be employed, this modification being suitable for concave or convex cylindrical surfaces.

The mounting of the pick-up head C adjustably in the framework A may also be modified, for example by employing a ligament hinge for the pivot or by dispensing altogether with the pivot and providing limited play by means of a spring connection between the pick-up head (3 and the adjustable rod B or casing E. Such arrangejment is shown in Figures 4 and 5.

In this arrangement the adjustable rod B is provided at its lower end with a cross-bar B ex= tending along the length of the framework A,

' and the pick-up head C is suspended from this cross-bar by means of a pair of fiat links J connected to the cross-bar and to the head by flat ligament spring J, the arrangement constituting a parallelogram linkage constraining the pick-up head C to move substantially in the desired straight line path'within the limits of the very short traversing movement required. Since the ligaments-J and links J are substantially rigid K. Thus as the motor rotates the pick-up head C is driven forwards and backwards through its traversing drive and its return stroke.

Figure 4 also serves to show diagrammatically the electrical leads to the parts within the framework, these leads being taken out through the rod B, which is made hollow for the purpose. Thus the leads L from the piezo-electric crystal or other detector device in the pick-up head C pass through the rod B to the apparatus diagrammatically indicated at L comprising the indicating instrument and the amplifier and other parts of the electrical system for conveying the electrical energy from the detector device to such instrument. The leads M from the shunt-wound electric motor in the casing E are likewise taken out through the rod B to the D. C. source M supplying the motor. In the example illustrated the circuits are such as to permit the motor to be driven at will at either of the two different speeds, so that the unit can be employed in conjunction with an average meter and a pen-recorder, in a'manner analogous to that described in the prior specification above mentioned. Thus a resistance M is connected across the source M and a switch M is provided to enable the armature winding of the motor to be connected, as desired, either across the whole of the resistance M or across only a part of such resistance.

In the foregoing arrangements the vertical movement of the adjustable rod B, to bring the pick-up head C into the correct position relatively to the test surface, is controlled by a handoperated knurled nut. If desired, however, the

.necessary adjustment can be effected automatically by means of a spring. Figure 6 shows a modification of the arrangement of Figures 4 and 5 to give such automatic adjustment. In this modification the actuating nut B is omitted, and a spring 13 is inserted between the upper end of the rod B and the closed upper end of the framework boss A extended upwardly for the purpose. In this case, it is sometimes preferable to provide a counter weight B? driven through a rack and pinion connection 13 from the rod B, thereby ensuring that the working pressure of the skid is determined by the spring B independently of gravity.

Figures 7 and 8 show a further alternative employing similar automatic adjustment of the bar B by means of the springs B but in this case as applied to a pick-up head pivoted to a lever F as in Figure 3. In the example shown, the lever F is illustrated by way of variant as carrymg a roller K driven by a heart-shaped cam K,

as in Figures-4 and 5, instead of by the driving face. This foot may be provided on the head instead of on the lever F, if desired.

It will be appreciated that the foregoing -ar-. rangements have been described by way of example only and that the invention may be carried into practice in other ways. Thus although it has been assumed in the above description that the traversing line on the test surface lies horizontally, this is not essential to the invention, and the surface may lie at any desired angle, the framework being held in engagement with it by hand pressure.

What I claim as my invention and desire to secure by Letters Patent is:

l. A pick-up unit for use in apparatus for measuring or indicating roughnesses or undulations of, a cylindrical surface, comprising a light supporting framework having widely spaced supporting elements adapted to be held in engagement with the test surface at points lying on two straight lines parallel to the axis of such surface, a'member adjustably mounted in the framework, means for adjusting such member in a direction approximately normal to the test surface, a pick-up head supported with a limited amount of play by the adjustable member, a styluscarried by the pick-up head for traversing over the test surface along a generator thereof, and means carried by the pick-up head affording a datum for the measuring movements of the stylus approximately normal to the test surface during traversing.

2. Apick-up unit as claimed in claim 1, in which means are provided for pivotally connecting the pick-up head to the adjustable member at a point remote-from the stylus.

3. A pick-up unit as claimed in claim 1, in

which means are provided for resiliently support.-

'stylus carried by said head adapted to traverse over the surface to be tested, means carried by said head afiording a datum for the measuring movements of the stylus, a light supporting framework for said pick-up head having widely spaced supporting elements adapted to be held in engagement, with the surface to be tested,

and means for adjusting the pick-up head relatively to the said supporting elements in a direction'substantially parallel to the working movements of the stylus, said elements bzing so disposed that, when they are held in engagement with a cylindrical surface, the measuring movements of the stylus in all positions of adjustment of the pick-up head will be constrained to take place along a line which approximately intersects the axis of such cylindrical surface.

6. The combination with the features set forth in claim 5, of means supported by the framework for driving the pick-up head relatively to the framework whereby the stylus is caused to be traversed over the test surface.

7 A pick-up unit for use in apparatus for measuring or indicating roughnesses or undulations of a cylindrical surface, comprising a light upporting framework having widely spaced supporting elements adapted to be held in engagement with the test surface at points lying on two straight lines parallel to the axis of such surface, a member adjustably mounted to the framework, means for adjusting such member in a direction approximately normal to the test surface, a pickup head supported with a, limited amount of play, by the adjustable member, a stylus carried by the pick-up head, means for driving the pick-up head relatively to the framework whereby the stylus is caused to be traversed over the test surface along a generator thereof, and a casing carried by the adjustable member for housing such driving means.

8. A pick-up unit as claimed in claim 7, in

which the means for driving the pick-up head relatively to the framework includes an escapement mechanism housed within the casing.

9. A pick-up unit as claimed in claim 7, in which the means for driving the pick-up head relatively to the framework comprises an electric motor housed within the casing.

10. A pick-up unit as claimed in claim 'I, in which the means for driving the pick-up head relatively to the framework comprises an electric motor housed within the casing, and a device for controlling the speed of the motor whereby the stylus can be traversed over the test surface at any one of a plurality of'difierent speeds.

11. A pick-up unit as claimed in claim 7, in which the pick-up head is connected 'to the adjustable member by means of flat ligaments arranged to constitute a parallelogram linkage.

12. A pick-up unit as claimed in claim 1, in which the pick-up head is connected to the adjustable member by means of flat ligament springs arranged to constitute a parallelogram linkage, and the adjusting means includes a spring acting to urge the adjustable member towards the test surface relatively'to the framework.

13.11 pick-up unit as claimed in claim '1,

wherei the pick-up head-driving means is a variable speed mechanism, whereby traverse of .the'stylils is at a selected one of a plurality of eluding automatic actuating means operating the adjusting means to urge said adjustable member toward the surface to be tested.

15. A pick-up unit as ,claimedin claim 7, in-

cluding automatic actuating means operating the adjusting means to urge said adjustable member toward the surface to betested.

" RICHARD'EDMUND REASON.

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